You control a permanent that can tap to produce at least ({U} magic symbol) .
Steps
Activate the mana-producing permanent by tapping it, adding ({U} magic symbol) .
Activate
Fatestitcher's unearth ability by paying ({U} magic symbol) , returning it from your graveyard to the battlefield and giving it haste until end of turn.
Activate
Fatestitcher by tapping it, untapping the mana-producing permanent.
Activate
Altar of Dementia by sacrificing
Fatestitcher.
Choose to exile
Fatestitcher using
Void Maw's replacement effect instead of
Fatestitcher's.
Resolve the
Altar of Dementia ability, causing target player to mill cards equal to
Fatestitcher's power.
Activate
Void Maw by putting
Fatestitcher from exile into your graveyard, giving